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[PATCH v33 04/11] Add Incremental View Maintenance support to pg_dump 199+ messages / 2 participants [nested] [flat]
* [PATCH v33 04/11] Add Incremental View Maintenance support to pg_dump @ 2020-11-11 08:01 Yugo Nagata <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Yugo Nagata @ 2020-11-11 08:01 UTC (permalink / raw) Support CREATE INCREMENTAL MATERIALIZED VIEW syntax. --- src/bin/pg_dump/pg_dump.c | 18 +++++++++++++++--- src/bin/pg_dump/pg_dump.h | 2 ++ src/bin/pg_dump/t/002_pg_dump.pl | 18 ++++++++++++++++++ 3 files changed, 35 insertions(+), 3 deletions(-) diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c index e324070828..c2e1f761dc 100644 --- a/src/bin/pg_dump/pg_dump.c +++ b/src/bin/pg_dump/pg_dump.c @@ -6740,6 +6740,7 @@ getTables(Archive *fout, int *numTables) int i_relacl; int i_acldefault; int i_ispartition; + int i_isivm; /* * Find all the tables and table-like objects. @@ -6842,10 +6843,17 @@ getTables(Archive *fout, int *numTables) if (fout->remoteVersion >= 100000) appendPQExpBufferStr(query, - "c.relispartition AS ispartition "); + "c.relispartition AS ispartition, "); else appendPQExpBufferStr(query, - "false AS ispartition "); + "false AS ispartition, "); + + if (fout->remoteVersion >= 170000) + appendPQExpBufferStr(query, + "c.relisivm AS isivm "); + else + appendPQExpBufferStr(query, + "false AS isivm "); /* * Left join to pg_depend to pick up dependency info linking sequences to @@ -6954,6 +6962,7 @@ getTables(Archive *fout, int *numTables) i_relacl = PQfnumber(res, "relacl"); i_acldefault = PQfnumber(res, "acldefault"); i_ispartition = PQfnumber(res, "ispartition"); + i_isivm = PQfnumber(res, "isivm"); if (dopt->lockWaitTimeout) { @@ -7033,6 +7042,7 @@ getTables(Archive *fout, int *numTables) tblinfo[i].amname = pg_strdup(PQgetvalue(res, i, i_amname)); tblinfo[i].is_identity_sequence = (strcmp(PQgetvalue(res, i, i_is_identity_sequence), "t") == 0); tblinfo[i].ispartition = (strcmp(PQgetvalue(res, i, i_ispartition), "t") == 0); + tblinfo[i].isivm = (strcmp(PQgetvalue(res, i, i_isivm), "t") == 0); /* other fields were zeroed above */ @@ -15906,9 +15916,11 @@ dumpTableSchema(Archive *fout, const TableInfo *tbinfo) binary_upgrade_set_pg_class_oids(fout, q, tbinfo->dobj.catId.oid, false); - appendPQExpBuffer(q, "CREATE %s%s %s", + appendPQExpBuffer(q, "CREATE %s%s%s %s", tbinfo->relpersistence == RELPERSISTENCE_UNLOGGED ? "UNLOGGED " : "", + tbinfo->relkind == RELKIND_MATVIEW && tbinfo->isivm ? + "INCREMENTAL " : "", reltypename, qualrelname); diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h index 865823868f..7eac1e7c6f 100644 --- a/src/bin/pg_dump/pg_dump.h +++ b/src/bin/pg_dump/pg_dump.h @@ -325,6 +325,8 @@ typedef struct _tableInfo int numParents; /* number of (immediate) parent tables */ struct _tableInfo **parents; /* TableInfos of immediate parents */ + bool isivm; /* is incrementally maintainable materialized view? */ + /* * These fields are computed only if we decide the table is interesting * (it's either a table to dump, or a direct parent of a dumpable table). diff --git a/src/bin/pg_dump/t/002_pg_dump.pl b/src/bin/pg_dump/t/002_pg_dump.pl index d3dd8784d6..62fc9b5bc4 100644 --- a/src/bin/pg_dump/t/002_pg_dump.pl +++ b/src/bin/pg_dump/t/002_pg_dump.pl @@ -2785,6 +2785,24 @@ my %tests = ( }, }, + 'CREATE MATERIALIZED VIEW matview_ivm' => { + create_order => 21, + create_sql => 'CREATE INCREMENTAL MATERIALIZED VIEW dump_test.matview_ivm (col1) AS + SELECT col1 FROM dump_test.test_table;', + regexp => qr/^ + \QCREATE INCREMENTAL MATERIALIZED VIEW dump_test.matview_ivm AS\E + \n\s+\QSELECT col1\E + \n\s+\QFROM dump_test.test_table\E + \n\s+\QWITH NO DATA;\E + /xm, + like => + { %full_runs, %dump_test_schema_runs, section_pre_data => 1, }, + unlike => { + exclude_dump_test_schema => 1, + only_dump_measurement => 1, + }, + }, + 'CREATE POLICY p1 ON test_table' => { create_order => 22, create_sql => 'CREATE POLICY p1 ON dump_test.test_table -- 2.25.1 --Multipart=_Tue__2_Jul_2024_17_03_11_+0900_6OrVBZxOB4o_k6A1 Content-Type: text/x-diff; name="v33-0003-Allow-to-prolong-life-span-of-transition-tables-.patch" Content-Disposition: attachment; filename="v33-0003-Allow-to-prolong-life-span-of-transition-tables-.patch" Content-Transfer-Encoding: 7bit ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 133 ++++++++++++++++++++++++++-- 2 files changed, 125 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fd7e21d96d3..de755fd53ad 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,41 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if (buf_state & BM_IO_IN_PROGRESS) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1724,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1743,38 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (operation->foreign_io) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1860,56 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses + * of an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + */ + if (1 && ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + /* FIXME: probably need to wait if io_method == sync? */ + + *nblocks_progress = 1; + did_start_io = true; + operation->foreign_io = true; + + if (0) + elog(LOG, "using foreign IO path"); + + /* FIXME: trace point */ + + /* + * FIXME: how should this be accounted for in stats? Account as a hit + * for now, quite likely *we* started this IO. + */ + if (persistence == RELPERSISTENCE_TEMP) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + + return true; + } + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1967,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O in progress in another backend (it can't be this + * backend), we want to wait for the outcome: either done, or something + * went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { @@ -1970,6 +2082,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; + operation->foreign_io = false; *nblocks_progress = io_buffers_len; did_start_io = true; } @@ -5986,6 +6099,8 @@ WaitIO(BufferDesc *buf) */ if (pgaio_wref_valid(&iow)) { + if (0) + elog(LOG, "foreign wait"); pgaio_wref_wait(&iow); /* -- 2.48.1.76.g4e746b1a31.dirty --j4imdtjxqt5tb6mo-- ^ permalink raw reply [nested|flat] 199+ messages in thread
* [PATCH v2 3/3] bufmgr: aio: Prototype for not waiting for already-in-progress IO @ 2025-08-15 15:01 Andres Freund <[email protected]> 0 siblings, 0 replies; 199+ messages in thread From: Andres Freund @ 2025-08-15 15:01 UTC (permalink / raw) Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 150 ++++++++++++++++++++++++++-- 2 files changed, 142 insertions(+), 9 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 41fdc1e7693..7ddb867bc99 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -137,6 +137,7 @@ struct ReadBuffersOperation int flags; int16 nblocks; int16 nblocks_done; + bool foreign_io; PgAioWaitRef io_wref; PgAioReturn io_return; }; diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fe470de63f2..7b245daaf4e 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1557,6 +1557,46 @@ ReadBuffersCanStartIOOnce(Buffer buffer, bool nowait) return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait); } +/* + * Check if the buffer is already undergoing read AIO. If it is, assign the + * IO's wait reference to operation->io_wref, thereby allowing the caller to + * wait for that IO. + */ +static inline bool +ReadBuffersIOAlreadyInProgress(ReadBuffersOperation *operation, Buffer buffer) +{ + BufferDesc *desc; + uint32 buf_state; + PgAioWaitRef iow; + + pgaio_wref_clear(&iow); + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + if ((buf_state & BM_IO_IN_PROGRESS) && !(buf_state & BM_VALID)) + iow = desc->io_wref; + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + + if ((buf_state & BM_IO_IN_PROGRESS) && !(buf_state & BM_VALID)) + iow = desc->io_wref; + UnlockBufHdr(desc, buf_state); + } + + if (pgaio_wref_valid(&iow)) + { + operation->io_wref = iow; + return true; + } + + return false; +} + /* * Helper for AsyncReadBuffers that tries to get the buffer ready for IO. */ @@ -1689,7 +1729,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) * * we first check if we already know the IO is complete. */ - if (aio_ret->result.status == PGAIO_RS_UNKNOWN && + if ((operation->foreign_io || aio_ret->result.status == PGAIO_RS_UNKNOWN) && !pgaio_wref_check_done(&operation->io_wref)) { instr_time io_start = pgstat_prepare_io_time(track_io_timing); @@ -1708,11 +1748,66 @@ WaitReadBuffers(ReadBuffersOperation *operation) Assert(pgaio_wref_check_done(&operation->io_wref)); } - /* - * We now are sure the IO completed. Check the results. This - * includes reporting on errors if there were any. - */ - ProcessReadBuffersResult(operation); + if (unlikely(operation->foreign_io)) + { + Buffer buffer = operation->buffers[operation->nblocks_done]; + BufferDesc *desc; + uint32 buf_state; + + if (BufferIsLocal(buffer)) + { + desc = GetLocalBufferDescriptor(-buffer - 1); + buf_state = pg_atomic_read_u32(&desc->state); + } + else + { + desc = GetBufferDescriptor(buffer - 1); + buf_state = LockBufHdr(desc); + UnlockBufHdr(desc, buf_state); + } + + if (buf_state & BM_VALID) + { + operation->nblocks_done += 1; + Assert(operation->nblocks_done <= operation->nblocks); + + /* + * Report and track this as a 'hit' for this backend, even + * though it must have started out as a miss in + * PinBufferForBlock(). The other backend (or ourselves, + * as part of a read started earlier) will track this as a + * 'read'. + */ + TRACE_POSTGRESQL_BUFFER_READ_DONE(operation->forknum, + operation->blocknum + operation->nblocks_done, + operation->smgr->smgr_rlocator.locator.spcOid, + operation->smgr->smgr_rlocator.locator.dbOid, + operation->smgr->smgr_rlocator.locator.relNumber, + operation->smgr->smgr_rlocator.backend, + true); + + if (BufferIsLocal(buffer)) + pgBufferUsage.local_blks_hit += 1; + else + pgBufferUsage.shared_blks_hit += 1; + + if (operation->rel) + pgstat_count_buffer_hit(operation->rel); + + pgstat_count_io_op(io_object, io_context, IOOP_HIT, 1, 0); + + if (VacuumCostActive) + VacuumCostBalance += VacuumCostPageHit; + } + } + else + { + /* + * We now are sure the IO completed. Check the results. This + * includes reporting on errors if there were any. + */ + ProcessReadBuffersResult(operation); + } } /* @@ -1798,6 +1893,43 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) io_object = IOOBJECT_RELATION; } + /* + * If AIO is in progress, be it in this backend or another backend, we + * just associate the wait reference with the operation and wait in + * WaitReadBuffers(). This turns out to be important for performance in + * two workloads: + * + * 1) A read stream that has to read the same block multiple times within + * the readahead distance. This can happen e.g. for the table accesses of + * an index scan. + * + * 2) Concurrent scans by multiple backends on the same relation. + * + * If we were to synchronously wait for the in-progress IO, we'd not be + * able to keep enough I/O in flight. + * + * If we do find there is ongoing I/O for the buffer, we set up a 1-block + * ReadBuffersOperation that WaitReadBuffers then can wait on. + * + * It's possible that another backend starts IO on the buffer between this + * check and the ReadBuffersCanStartIO(nowait = false) below. In that case + * we will synchronously wait for the IO below, but the window for that is + * small enough that it won't happen often enough to have a significant + * performance impact. + */ + if (ReadBuffersIOAlreadyInProgress(operation, buffers[nblocks_done])) + { + *nblocks_progress = 1; + operation->foreign_io = true; + + CheckReadBuffersOperation(operation, false); + + + return true; + } + + operation->foreign_io = false; + /* * If zero_damaged_pages is enabled, add the READ_BUFFERS_ZERO_ON_ERROR * flag. The reason for that is that, hopefully, zero_damaged_pages isn't @@ -1855,9 +1987,9 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress) /* * Check if we can start IO on the first to-be-read buffer. * - * If an I/O is already in progress in another backend, we want to wait - * for the outcome: either done, or something went wrong and we will - * retry. + * If a synchronous I/O is in progress in another backend (it can't be + * this backend), we want to wait for the outcome: either done, or + * something went wrong and we will retry. */ if (!ReadBuffersCanStartIO(buffers[nblocks_done], false)) { -- 2.48.1.76.g4e746b1a31.dirty --aknbaqiolq3mrqjk-- ^ permalink raw reply [nested|flat] 199+ messages in thread
end of thread, other threads:[~2025-08-15 15:01 UTC | newest] Thread overview: 199+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2020-11-11 08:01 [PATCH v33 04/11] Add Incremental View Maintenance support to pg_dump Yugo Nagata <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v2 3/3] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]> 2025-08-15 15:01 [PATCH v1] bufmgr: aio: Prototype for not waiting for already-in-progress IO Andres Freund <[email protected]>
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